This application is based on Japanese Patent Application No. 11-272974, filed Sep. 27, 1999, and Japanese Patent Application No. 11-272975, filed Sep. 27, 1999. The entire contents of these patents are hereby expressly incorporated by reference.
1. Field of the Invention
The present invention generally relates to a combustion control system for a two-cycle engine. More specifically, the present invention relates to an improved fuel injection system and an improved method for operating a fuel injection system.
2. Related Art
Personal watercraft have become very popular in recent years. This type of watercraft is quite sporting in nature and carries one or more riders. Due to space limitations and power demands, personal watercraft typically are powered by two-stroke engines. Two-stroke engines include an exhaust port provided in each cylinder wall such that spent gases are exhausted through the exhaust port as the piston reciprocates in the cylinder. The timing of the opening and closing of the exhaust port has an important effect on engine performance. Exhaust port timing can be adjusted with exhaust control valves. Optimum exhaust port timing is dependent, in part, upon engine speed. For instance, to improve engine performance, the exhaust port timing typically is advanced during high-speed/high-load engine operation (e.g., engine speeds greater than 6000 RPM) relative to the exhaust port timing during engine idling or low-speed/low-load operation. In other words, the valve is xe2x80x9copenedxe2x80x9d during high-speed/high-load operation and xe2x80x9cclosedxe2x80x9d during low-speed/low-load operation. This results in lower compression ratios at high-speed/high-load conditions, which reduces the pressure in the combustion chamber and inhibits some pre-ignition or knocking conditions. Correspondingly, by delaying exhaust port timing during idling or low-speed/low-load conditions, higher compression ratios result, which typically improve engine performance at low-speed/low-load conditions.
As discussed above, one manner of controlling exhaust port timing is to employ exhaust timing control valves. Generally, these valves are of the sliding or rotating type and do not serve to ever completely close the opening or port in each combustion chamber in two-stroke applications. Instead, each valve moves between a first position, in which the valve does not obstruct, or obstructs very little of, the exhaust port, and a second position, in which the valve partially obstructs the port. Therefore, the exhaust control valve can alter the effective cross-sectional area of the exhaust port by appearing to lower an upper surface of the exhaust port, thereby restricting the flow through the exhaust port. This alters the timing of the opening and closing of the exhaust ports. That is, by retracting the exhaust control valve into the exhaust port, it is possible to advance exhaust port timing. In a similar manner, by extending the exhaust control valve into the exhaust port, it is possible to delay exhaust port timing. The engine control system usually is configured to retract the exhaust valve when the engine speed/load increases beyond a specified value (e.g., 6000 RPM) and to extend the exhaust control valve when the engine speed/load decreases beyond the certain value.
Personal watercraft usually begin to plane at approximately 2000-3500 RPM. While planing, it is not uncommon for the personal watercraft to jump out of the water. When this occurs, the engine speed suddenly increases because of the hull is no longer substantially affected by water resistance. Moreover, when the watercraft lands on the water, the engine speed suddenly slows down due to the sudden increase in the water resistance. These sudden changes in engine speed can cause the engine to stall or can cause irregular combustion within the engine.
To improve emissions, personal watercraft typically include a catalyst for cleaning the exhaust gases. The catalyst typically is not activated until the temperature of the exhaust gas entering the catalyst reaches 250-300 C. To achieve this temperature in the exhaust gas, the watercraft typically needs to be traveling around 25 Km/hour (i.e., a planing speed with an engine speed more than 2000-3500 RPM). However, near shore and/or in swimming areas, personal watercraft typically must be operated below a certain speed (e.g. below 10 km/hour). At these speeds, the exhaust gas temperature is usually about 100 C., which is insufficient to activate the catalyst. Thus, the exhaust gas cannot be adequately cleaned near shore and/or in swimming areas.
An aspect of the present invention is the recognition that the tendency of the watercraft to stall or to experience irregular combustion during jumping and landings is caused, at least, in part by the movement of the exhaust control valves. Specifically, in personal watercraft, the exhaust control valves typically are driven by a servo-motor, which is controlled by the engine control system. The engine control system generally is configured to open or close the exhaust control valve when the engine speed increases or decreases beyond a specified engine speed (e.g., 6000 RPM). However, the servo-motor typically experiences a response delay on the order of one to two seconds.
This response delay can result in engine stalling and/or irregular combustion. For instance, when the watercraft jumps out of the water, the engine speed increases quickly and the engine control system, in response, delivers more fuel to the engine and opens the exhaust valve. However, because of the response delay, the exhaust control valve is only partially opened when more fuel is delivered to the engine. Nevertheless, less air enters the combustion chamber because the valve obstructs exhaust gas flow from combustion chamber. This results in a rich air/fuel ratio, which can cause irregular combustion. Correspondingly, when the watercraft is landing, the engine speed decreases quickly and the engine controls system delivers less fuel to the engine and closes the exhaust valve. However, because of the response delay, the control valve is partially opened while less fuel is delivered to the engine. Thus, too much air enters the combustion chamber in comparison to the amount of fuel being delivered to the engine. This results in a lean air/fuel ratio, which can cause the engine to stall.
Accordingly, one aspect of the present invention involves a two-cycle, internal combustion engine. The engine comprises a cylinder block that defines a cylinder bore. A cylinder head is fixed at one end of the cylinder block and encloses one end of the cylinder bore. A crankcase member is fixed at the other end of the cylinder block and encloses the other end of the cylinder bore. The crankcase member forms a crankcase chamber. A piston is positioned in the cylinder bore. A crankshaft is rotably journaled in the crankcase and is driven by the piston. The piston, the cylinder bore, and the cylinder head together define a combustion chamber. At least one scavenge passage is formed in the cylinder block for transferring an air charge compressed in the crankcase to the combustion chamber. The scavenge passage comprises a scavenge port configured such that reciprocating motion of the piston opens and closes the scavenge port. An exhaust passage is formed in the cylinder block for discharging exhaust gases from the combustion chamber. The exhaust passage includes an exhaust port configured such that the reciprocating motion of the piston opens and closes the exhaust port. A fuel injector is mounted to inject fuel directly into the combustion chamber. The fuel injector includes an actuator to regulate an amount of fuel injected by the fuel injector, an exhaust control valve extends into the exhaust passage and is adapted to control the effective cross-sectional area of the exhaust port. An exhaust control valve position sensor a senses the position of the exhaust control valve. The position sensor is electronically connected to a control system. The control system includes a controller that is configured to control the position of the exhaust control valve, the amount of fuel injected by the fuel injector, and to receive a signal from the exhaust control valve position sensor. The controller is also configured to increase the effective cross-sectional area of the exhaust port when an engine speed increases beyond a specified value and to adjust the amount of fuel injected into the combustion chamber based upon the sensed position of the exhaust control valve.
Another aspect of the present invention involves a method of operating a two-cycle internal combustion engine. The method includes sensing a position of an exhaust control valve. An engine speeds is also sensed. The amount of fuel injected by a fuel injector is adjusted based upon the sensed position of the exhaust control valve and the engine speed.
Yet another aspect of the present invention involves a two-cycle internal combustion engine. The engine comprises a cylinder block that defines a cylinder bore. A cylinder head is fixed at one end of the cylinder block and encloses one end of the cylinder bore. A crankcase member is fixed at the other end of the cylinder block and encloses the other end of the cylinder bore. The crankcase member defines a crankcase chamber. A piston is positioned in the cylinder bore. A crankshaft is rotably journaled in the crank case and is driven by the piston. The piston, the cylinder bore, and the cylinder head together define a combustion chamber. At least one scavenge passage is formed in the cylinder block for transferring an air charge compressed in the crankcase to the combustion chamber. The scavenge passage comprises a scavenge port configured such that reciprocating motion of the piston opens and closes the scavenge port. An exhaust passage is formed in the cylinder block for discharging exhaust gases from the combustion chamber. The exhaust passage comprises an exhaust port configured such that the reciprocating motion of the piston opens and closes the exhaust port. A fuel injector is disposed to inject fuel directly into the combustion chamber. The fuel injector includes an actuator. An exhaust control valve is operatively mounted in the exhaust passage and adapted to vary the effective cross-sectional area of the exhaust port. An exhaust control valve position sensor senses a position of the exhaust control valve is in electrical communication with a control unit. An exhaust system connected to the combustion chamber includes a catalyst. The engine further including means for increasing a temperature of the catalyst when the engine is operating at an engine speed less than a specified speed.
Still yet another aspect of the present invention is a method of controlling a two-cycle engine. The method comprises sensing a position of an exhaust control valve and sensing an engine speed. At least two injection characteristic maps are consulted. One of said at least two injection characteristic maps are selected. An injection characteristic is controlled based upon said selected one of said at least two injection characteristic maps.
Another aspect of the present invention is a method of increasing an operating temperature of a catalyst. The method comprises sensing an operating speed of an engine and adjusting a fuel injection characteristic when said engine is operating below a preset speed. The fuel injection characteristic being selected to create a fuel rich air/fuel charge within a combustion chamber.